The present invention relates to the field of recycling used tires. More particularly, the present invention relates to a method of processing used tires and the recovery of products thereof.
The recycling of used tires and the recovery of component products is known in the art. However, many previous methods have sought to reclaim only a single product. This strategy has been used where it is economically feasible to recover the component product to be reclaimed. Other methods have reprocessed used tires with the idea of converting the resulting component products into new functional materials. Some processes have sought to reprocess the used tires into crude oil, while others have attempted to reprocess used tires into rubber strips or useful resins.
Schmidt, U.S. Pat. No. 5,127,588 discloses a machine for reducing vehicle tires to small chip-like particles. The Schmidt "tire chipper" is representative of the first step in the process used to reclaim materials from used tires.
In Stapp, U.S. Pat. No. 5,158,983, a process for converting tire scrap to useful oil, especially crude oil, is disclosed. This process uses a hydrogen atmosphere and a temperature of approximately 350.degree. C.-450.degree. C. This process also utilizes a preferred pressure of 750-3,000 psi and a preferred processing time between 30 minutes and 4 hours. This process is representative of the high energy input required for the reprocessing of used automobile tires. Further, the presence of a hydrogen atmosphere, in combination with the high temperatures, presents a potentially dangerous processing method.
Johnson, et al., U.S. Pat. No. 2,478,826, discloses a method of reclaiming Buna N type rubber (synthetic rubber) by means of using phenyl-beta-naphthylamine, at atmospheric pressure, at approximately 250.degree. F.-350.degree. F. for 6-10 hours. This process also utilizes a pressure of approximately 60-75 psia. This process represents a way of reclaiming synthetic rubber, however, it does not teach the reprocessing of used automobile tires.
In Price, U.S. Pat. No. 693,151, a process for reclaiming rubber from vulcanized rubber waste is disclosed. The Price process utilizes a superheated fluid to bathe the vulcanized rubber waste which is heated to approximately 300.degree. C.-450.degree. C. This process uses high temperatures and low pressures due to the superheated fluid. The liquid bath contains hyposulfite of soda which has the effect of preventing further oxygenation of the rubber waste, which would produce a further vulcanization. The soda solution also functions to remove the sulfur from the rubber waste. However, this process is a closed process utilizing superheated steamed heat and as such presents the dangers associated with such processes.
Merges, U.S. Pat. No. 3,460,769, discloses a method and apparatus for reclaiming rubber scrap. The Merges method also discloses the use of swelling additives, like oil, and the use of heat in order to plasticize the scrap material. However, the Merges process discloses the use of centrifugal forces which simultaneously expose the scrap in a pulsating manner to friction, milling, shearing, and crushing forces. Further, the Merges process does not disclose the optimization of the swelling procedure, nor does it describe the different properties of the swelling agents.
In Massoubre, U.S. Pat. No. 3,563,922, a method of regenerating vulcanized rubber, resulting products, and compositions containing the regenerating products, is disclosed. The process described includes the steps of taking the finely divided vulcanized rubber, using a swelling agent to plasticize the rubber, adding a devulcanization agent to the rubber, and heating the rubber and solvent mixture within the temperature range of 180.degree. C.-230.degree. C. for two to three hours. The oil used as plasticizer is used in a ratio in the preferred embodiment of 65%-100% oil to scrap. The Massourbre process discloses solvents which include mineral oils obtained by the distillation of petroleum oil or coal, vegetable and animal oils consisting of the glyceric esters of fatty acids, and compounds of the above oils. The vegetable and animal oils disclosed are castor oil and paraffin. In the examples disclosed, both the vegetable and animal oils are used in combination with mineral oils. The Massoubre process requires subjecting the scrap to relatively low temperatures, for long periods of time, and in the presence of large amounts of oil as seen in the oil to scrap ratio.